Single blood eosinophil measure predicts eosinophilic asthma
medwireNews: A single blood eosinophil count could predict persistent eosinophilia in patients with adult-onset asthma, study findings show.
“By using two cut-off points we could classify 74% of the patients into the ‘eosinophilic’ or ‘non eosinophilic’ phenotype, with an accuracy of 93%,” the researchers report in Respiratory Medicine. “These cut-off values may become very useful for clinical application of personalized treatments and implementation of the ‘treatable traits’ approach.”
As part of the ADONIS-project, 114 adults diagnosed with asthma less than 12 months previously were assessed at baseline, 6 months, 12 months, and yearly thereafter for up to 5 years. At each assessment, the patients’ peripheral blood cell counts and exhaled nitric oxide (FeNO) levels were measured, their exacerbations recorded, and they completed the asthma control questionnaire.
Blood eosinophil counts were measured at thresholds of either at or above 0.30 x 109/L or at or above 0.40 x 109/L.
In all, 9% of the patients had persistent blood eosinophil levels of at least 0.30 x 109/L, while 72% had persistent levels below this cutoff.
Receiver operating characteristic curve analysis showed that a single measurement of blood eosinophils could significantly predict eosinophilic asthma at this level with an area under the curve of 0.89 (95% confidence interval [CI] of 0.73–1.00).
The same was true for persistent blood eosinophil levels at or above 0.40 x 109/L, which was seen in 7% of patients. One single blood measurement predicted eosinophilic asthma at this level with an area under the curve of 0.79 (95% CI of 0.39–1.00).
The cutoff values in each case were 0.47 x 109/L for blood eosinophil levels of at least 0.30 x 109/L and 0.49 x 109/L for levels at or above 0.40 x 109/L. At these cut-offs, the positive predictive values for diagnosing eosinophilic asthma were 83% and 80%, respectively.
This compared with a positive predictive value of around 40% when FeNO, at a cut-off value of at least 83 ppb, was used.
The less accurate diagnosis with FeNO is “remarkable,” say Hanneke Coumou (University of Amsterdam, the Netherlands) and co-investigators, “because FeNO is often associated with eosinophilic airway inflammation.”
They suggest that FeNo and blood eosinophils may “represent different pathways associated with airway eosinophilia.”
The investigators also measured sputum eosinophils at a threshold of 3% or above, but they found that not enough patients were able to provide a repeated sample for this to be used as a gold standard. Nevertheless, they point out that diagnostic cut-offs were similar for blood and sputum eosinophils and patients with consistent blood eosinophilia able to produce sputum also showed consistent sputum eosinophilia.
“Our study has clinical implications because it shows that in a large part of the adult-onset asthma patients ‘eosinophilic asthma’ can be diagnosed by using 2 cut-off values (high and low) of blood eosinophils,” say the researchers.
They highlight the importance of this to identify such patients at an early stage of disease so that they can be treated with eosinophil-targeting drugs, while also ruling out this type of treatment in symptomatic patients without eosinophilia.
By Lucy Piper
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